Abstract
The soluble proteins of C(3) and C(4) mesophyll chloroplasts and C(4) bundle sheath extracts have been analyzed by gel electrophoresis for fraction I protein. Gel scans of soluble protein from C(4) bundle sheath extracts and C(3) mesophyll chloroplasts showed typical fraction I protein peaks that could be identified by ribulose diphosphate carboxylase activity. No such peak was observed for C(4) mesophyll chloroplasts, which also lacked both large and small subunits of ribulose diphosphate carboxylase on sodium dodecyl sulfate gels. The absence of fraction I protein in these chloroplasts was reflected in the soluble protein to chlorophyll ratios, which were roughly 3-fold lower than the ratio obtained for C(3) chloroplasts. The carboxylating enzyme in C(4) mesophyll cells, phosphoenolpyruvate carboxylase, was found to be a major protein in the cytoplasm of C(4) mesophyll protoplasts, and had higher mobility than fraction I protein.